The present invention is concerned with improvements in or relating to the so-called green assembly process for joining together a plurality of green compacts into one sintered piece.
The conventional processes for making a mechanical part of a complicated profile comprises preparing separately a green compact having a projection or shaft (hereinafter referred to as the inner part) and a green compact having therein an associated recess or opening (hereinafter called the outer part) and fitting the shaft of the inner part into the associated opening of the outer part followed by sintering.
In accordance with such processes, the fitting of the inner part into the associated outer part is effected by the so-called shrink fit wherein an interference, viz., a difference in fitting size between the shaft and the opening, is fixed at a certain value resulting in interference fit, and the outer part is heated to expand the inner diameter thereof and fitted with the inner part in the thus expanded sate.
However, if the interference is too large, one would experience difficulty in the proper determination thereof due to the limited joining strength of the sintered body consisting of the inner and outer parts. This is also true where the interference is too small. Thus, there has been available only a limited interference.